1. Field of the Invention
This invention relates in general to a hybrid Internet Protocol-Asynchronous Transfer Mode (IP-ATM) networks, and more particularly to a method and apparatus for coupling IP explicit congestion notification (ECN) with ATM congestion control.
2. Description of Related Art
Today, an organization's computer network has become its circulatory system. Organizations have combined desktop work stations, servers, and hosts into Local Area Network (LAN) communities. These Local Area Networks have been connected to other Local Area Networks and to Wide Area Networks (WANs). It has become a necessity of day-to-day operation that pairs of systems must be able to communicate when they need to, without regard to where they may be located in the network.
During the early years of network computing, proprietary networking protocols were the standard. However, the development of the Open Systems Interconnection Reference Model introduced by the International Organization for Standardization (ISO) has led to an impressive degree of interworking, which generally allows end-user applications to work very well between systems in a network. Implementations are based on written standards that have been made available by volunteers from dozens of computer vendors, hardware component vendors and independent software companies.
During the last decade, LANs have been proliferating. This has created a recurring problem of how to minimize congestion and optimize throughput that must be solved by network managers. An early solution was to simply divide Local Area Networks into multiple smaller networks serving smaller populations. These segments were connected by bridges to form a single Local Area Network with traffic being segregated locally to each segment.
The evolution of new network types and Wide Area Networks created a need for routers. For example, the Internet is a set of networks connected by gateways, which are sometimes referred to as routers. Routers added filtering and firewalling capability to provide more control over broadcast domains, limit broadcast traffic and enhance security. A router is able to chose the best path through the network due to embedded intelligence. This added intelligence also allowed routers to build redundant paths to destinations when possible. Nevertheless, the added complexity of best path selection capability accorded by the embedded intelligence increased the port cost of routers and caused substantial latency overhead. Shared-media networks comprising distributed client/server data traffic, expanded user populations and more complex applications gave birth to new bandwidth bottlenecks. Such congestion produced unpredictable network response times, the inability to support the delay-sensitive applications and higher network failure rates.
The Internet Protocol (IP) is a network layer protocol that routes data across an Internet. The Internet Protocol was designed to accommodate the use of host and routers built by different vendors, encompass a growing variety of growing network types, enable the network to grow without interrupting servers, and support higher-layer of session and message-oriented services. The IP network layer allows integration of Local Area Network "islands".
Transmission Control Protocol (TCP) is a part of the TCP/IP protocol family that has gained the position as one of the world's most important data communication protocols with the success of the Internet. TCP provides a reliable data connection between devices using TCP/IP protocols. TCP operates on top of IP that is used for packing the data to data packets, called datagrams, and for transmitting across the network.
However, IP doesn't contain any flow control or retransmission mechanisms. That is why TCP is typically used on top of it. Especially, TCP uses acknowledgments for detecting lost data packets. TCP/IP networks are nowadays probably the most important of all networks, and operate on top of several (physical) networks. These underlying networks may offer some information about the condition of network and traffic, which may be used to provide feedback regarding congestion.
Asynchronous Transfer Mode (ATM) has become a successful and popular network technology because of its ability to transport legacy data traffic, mostly IP, over its network infrastructure. ATM is connection-oriented, that is, a connection need to established between two parties before they can send data to each other. Once the connection is set up, all data between them is sent along the connection path. On the contrary, IP is connectionless so that no connection is needed and each IP packet is forwarded by routers independently on a hop-by-hop basis. When we need to transport IP traffic over an ATM network, we have two options. Either a new connection is established on demand between two parties or the data is forwarded through preconfigured connection or connections. With the first approach, when the amount of data to be transferred is small, the expensive cost of setting up and tearing down a connection is not justified. On the other hand, with the second approach the preconfigured path(s) may not be an optimal path and may become overwhelmed by the amount of data being transferred.
Further, Quality of Service (QoS) is an important concept in ATM networks. QoS includes parameters such as bandwidth and delay requirements of a connection. Such requirements are included in the signaling messages used to establish a connection. However, Current IP (IPv4) has no such concepts and each packet is forwarded on a best effort basis by the routers. To take advantage of the QoS guarantees of the ATM networks, the IP protocol need to be modified to include that information.
Congestion control in today's Internet is increasingly becoming an important issue. The explosive growth of applications such as the World Wide Web (WWW) has pushed current technology to its limit, and it is clear that faster transport and improved congestion control mechanisms are required. As a result, many equipment vendors and service providers are turning to ATM technology to provide adequate solutions to the complex resource management issues involved. At the same time, there is a very large, concerted effort to improve the service offerings within IP networks themselves. This is clearly evidenced by the emergence of the IPv6 protocol specification, i.e., IP Next Generation, and the integrated and differentiated services models in the Internet Engineering Task Force (IETF). As a result, it is advantageous to design inter-working schemes which will be able to best leverage the advanced features of ATM technology to enhance the operation of the emerging next generation IP services over ATM networks.
Current IP networks cannot explicitly slow down, or even indicate congestion to, overloading data sources. For example, the ubiquitous TCP protocol relies on implicit congestion notification in the form of packet drops to detect network congestion, i.e., either via timeouts or duplicate acknowledgment packet (ACK) reception. Meanwhile, the UDP protocol even lacks such coarse indication methods. Recently, though, the Internet community is proposing the use of more advanced, faster congestion control mechanisms for the next generation of Internet services. A key such proposal emerging from the IETF is the differentiated services, i.e., DiffServ paradigm. On a very high level, this approach relies on packet classification (at the ingress) to label packets as belonging to one of several drop priorities. Network routers then rely on these labels to selectively process, i.e., buffer, drop, etc., packets during overload periods. The labels are identified via an 5-bit field in the Type of Service (TOS) byte specified in the IPv6 header, called the DS byte. In addition, two bits of this byte, the CU (currently unused) bits, have been reserved for future assignment. More specifically, these are for experimentation with explicit congestion notification (ECN) schemes. ECN is an attempt to directly incorporate network-bawd feedback into the IPv6 protocol. Similar strategies arc already available in the ATM and frame relay specifications.
For example, Sally Floyd and K. K. Ramakrishnan have submitted an Internet draft entitled "A Proposal To Add Explicit Congestion Notification (ECN) to IPv6 and to TCP" that proposes to use two CU bits to provide an indication of congestion: one bit is used to identify ECN-capable equipment and bit is used to actually indicate congestion. Overall, the results with ECN-TCP have shown improved performance over conventional implementations, especially with regards to end-to-end packet delays. By more effectively indicating congestion, queue levels can be maintained about reasonable operating levels thereby reducing buffering delays.
Although the above described proposals were directed towards TCP, more generic applications for future protocols are needed. For example, a similar one-bit IP ECN approach with additional Internet Control Message Protocol (ICMP) based extensions has also been proposed. As of yet, however, no bits have been formally reserved in the IPv6 header for ECN purposes.
It can be seen then that there is a need for a method and apparatus for coupling IP ECN with ATM congestion control.
It can also be seen that there is a need for a method and apparatus for extending IP ECN to ATM devices with minimal implementation complexity.
It can also be seen that there is a need for a method and apparatus for enhancing the performance of IP data traffic over ATM without requiring packet-reconstruction at the ATM layer.